This invention relates to traction drive torque transmissions and more particularly, it concerns improvements in the cooling and lubrication of traction surfaces of such transmissions.
In a commonly assigned U.S. Pat. No. 4,235,127, issued Nov. 25, 1980 to the present inventor, a traction surface cooling system for continuously variable torque transmissions is disclosed in which a traction surface lubricant is circulated into contact with the rolling traction surfaces in a manner to improve cooling. The traction surfaces are wiped either by blades or pads to remove boundary surface layers of the lubricant in a manner to enhance the transfer of heat from the surface to the lubricant.
Although the cooling system disclosed in the aforementioned patent is applicable to many diverse types of traction drive transmissions by which torque is transmitted between rolling surfaces retained against one another under high normal forces, it has been tested extensively with the type of transmission represented by the embodiment disclosed in the patent. In such transmissions, a nutatable beta body of biconical configuration is carried by a rotatable alpha body so that oppositely convergent conical surfaces on the beta body engage interior ring surfaces concentric with the axis of the alpha body at two diametrically opposite points of contact. The alpha body is in the nature of a truncated cylinder having a pair of frusto-conical pocketlike cavities to receive the conical portions of the beta body. To cool the conical surfaces of the beta body, the circulated lubricant is introduced in sufficient quantity to substantially flood the clearance space between the alpha body pockets and the conical surfaces. Because the internal traction surfaces on the rings are located outwardly of both the alpha body and the biconical beta body, cooling lubricant circulated to these surfaces is not as well defined and is primarily excess lubricant thrown outwardly by the rotating alpha and beta bodies. Both surfaces are wiped simultaneously with the circulation of lubricant to enhance heat exhange contact of lubricant with the surfaces.
Temperature monitoring of operating transmissions of the general type disclosed in the aforementioned patent has revealed that heat transfer from the pocketed conical surfaces on the beta body substantially exceeds the rate of heat transfer from the internal traction surfaces on the rings. The difference in cooling rates is believed due in substantial measure to the difference in the quantity of coolant circulated about the conical surfaces as compared with that brought into contact with the ring surfaces. Because the rings move axially in the transmission frame or housing and are both axially movable and rotatable relative to the alpha body in speed ratio varying operation of the transmission, however, a serious problem is presented in increasing the amount of coolant flow to the rings. There is a need, therefore, for a solution to this problem in transmissions of the type mentioned as well as in traction drive transmissions in general which have a comparable geometry.